1. Field of the Invention
The present invention relates to a laser generating apparatus and, more particularly, is directed to a laser generating apparatus of an SFG (Sum Frequency generation) type which generates a sum frequency of fundamental wave laser lights of first and second wavelengths by introducing these fundamental wave laser lights into a nonlinear optical device.
2. Description of the Prior Art
FIG. 1 of the accompanying drawings shows an example of a conventional laser generating apparatus of an SFG type which generates a sum frequency of laser lights having different wavelengths .lambda.1 and .lambda.2 emitted from first and second fundamental wave light sources 1 and 2 (see Applied Physics Letters, Vol. 52, p. 85, 1988 and Applied physics Letters, Vol. 54, p. 789, 1988).
This conventional laser generating apparatus of SFG type will be described below with reference to FIG. 1. As shown in FIG. 1, a nonlinear optical device 3 made of KTiOPO4 (KTP) for generating a sum frequency is provided within a laser resonator formed of mirrors 4M1 and 4M2 of a first fundamental wave light source 1.
The first fundamental wave light source 1 is an Nd:YAG laser excited by an excitation laser 5, for example, and a second fundamental wave light source 2 is a GaAlAs semiconductor laser. A laser light from the excitation laser 5 and a laser light from the second fundamental wave light source 2 are introduced through a polarization beam splitter (PBS) 6 into a resonator. A first fundamental wave based on the laser light having the first wavelength .lambda.1 from the Nd:YAG laser excited by the excitation laser light and a second fundamental wave based on the laser light having the second wavelength .lambda.2 from the fundamental wave light source 2 are introduced into the nonlinear optical device 3, in which the first and second fundamental waves are matched in phase in a type 2 fashion.
More specifically, when the first and second fundamental waves are introduced such that respective polarizing planes of the laser lights from the two fundamental wave light sources 1 and 2 are extended along a b-axis of a KTP crystal of the nonlinear optical device 3 and become coincident with an a-axis and a c-axis of the KTP crystal, this laser generating apparatus generates a blue coherent light beam having a short wavelength of .lambda.SFG=459 nm during the process for generating a sum frequency if .lambda.1=1064 nm and .lambda.2=809 nm on the basis of a relationship expressed as: EQU 1/.lambda.SFG=1/.lambda.1+1/.lambda.2 (1)
This laser light source apparatus of SFG type can modulate at a high speed GaAlAs laser that is used as the second fundamental wave light source. Therefore, it is expected that the laser light source apparatus of SFG type is suitably applied to a light source for optical memories because a sum frequency light can be modulated at a high speed by modulating the GaAlAs laser.
The conventional laser generating apparatus arranged as shown in FIG. 1, however, encounters problems, such as an insufficient conversion efficiency, an unstable output or the like.